A Black Horse spokesman said: “We are required to take note of every complaint we receive. Currently, the best way to do this quickly is to send a letter to the claims company so that it can be easily forwarded.

“However, we always recommend that customers contact us directly via our website, where they will find all the information they need to submit a complaint directly to us.”

Lloyds Bank is understood to be working with Courmacs Legal to find a solution that involves sending correspondence electronically.

Meanwhile, the Blackburn law firm has invested in new machines to open and scan the letters, assign them to the correct file and notify the lawyer handling the case.

Mr Smith said: “What should be a process to slow down the system, we’re doing quite well, but it’s been an investment on our part to make sure we can cope.”

Courmacs Legal represents 1.3 million consumers seeking compensation for mis-sold car loans. The firm operates a “no win, no fee” model and can receive up to 49% of rewards.

Plaintiff law firms complained that some large banks refused to provide all relevant information about commission arrangements with car dealers.

Elizabeth Comley, chief operating officer at Slater and Gordon, said lenders had “really dragged their feet” in providing the financial records required before a driver could start a claim for mis-sold car loans.

She warned of a “massive delay” as banks failed to respond to so-called subject access requests.

The Financial Conduct Authority last week extended the time car finance companies have to respond to a surge in complaints.